1. Field of the Invention
This invention relates to cells containing a liquid-alkali metal and to batteries formed of such cells and to the manufacture of such cells and batteries and is particularly applicable to sodium sulphur cells and batteries.
2. Prior Art
The sealing of sodium sulphur cells has been given considerable attention over the years because of the problems in effecting suitable seals. It has long been appreciated that cylindrical cells employing tubular solid electrolyte material has considerable advantages over flat plate cells. In a tubular cell, the construction may be of the central sodium type in which the electrolyte tube separates liquid sodium inside the tube from the sulphur/sodium polysulphides in an annular region between the outside of the electrolyte tube and a casing. In a central sulphur cell, the sulphr/sodium polysulphides lies inside the tube and the sodium is in the annular region between the electrolyte tube and the casing. In either case, a current collector has to extend outwardly from the central region. The electrolyte tube may be formed with one closed end but the other end has to be sealed around the current collector. Furthermore the annular region between the housing and the electrolyte tube must also be sealed. Current practice has been to secure an alpha alumina rigid ring around the open end of the electrolyte tube and to seal to this ring closure elements for closing both the sodium and the sulphur regions of the cell. Various techniques have been proposed and various forms of mechanical construction but these all require relatively large diameter seals between a metallic closure element and the alpha alumina ceramic ring.